Plastic closure caps made by injection molding are known and used in great numbers. There are many problems in mass production of such closure caps, which manufacture should be extraordinarily rapid and economical in view of the required low manufacturing cost. Many tools or molds used in the manufacture of such closure caps involve radially opening mold parts, which I consider to be much too expensive in production and maintenance, and additionally such parts work too slowly and are subject to malfunction and/or breakdown. Also, tools or molds for production of screw closures where the caps are turned or screwed out of the mold after completion of the injection process are believed not sufficiently competitive because of the high manufacturing and operating costs associated with them.
Quite special problems arise if closure caps are involved that have a guard ring or sealing ring which is to be heat-formed and sealed on the container. Such sealing rings are well known in themselves, and are sometimes referred to as tamper rings. Such rings are provided with a weakened zone or tear zone that is torn in the first opening movement of the cap from the bottle, and thus indicate whether or not the bottle has been opened or unsealed. These weakening lines increase the problems in manufacture of plastic closures of this kind, because there is a danger that a tear will be initiated along the weakening line in removal of the closure cap from the molding tool.
The instant invention is addressed to the problem of avoiding the drawbacks of known arrangements, and hence is directed particularly to methods and apparatus for production of a plastic closure cap device comprising a closure cap and sealing ring, and is intended to allow simple and quick production, together with reduced initial expenditure and subsequent maintenance costs for the apparatus.
Generally in accordance with the invention, a method is provided for molding a plastic closure cap unit for a container, the cap unit comprising an upper closure cap with a generally cylindrical wall portion including an inner surface with an integrally molded internal thread and an outer surface, the generally cylindrical wall portion having a downwardly extending integrally molded generally cylindrical skirt forming a sealing ring, and an intermediate shear zone having a reduced thickness in cross-section and forming a connection between the sealing ring and the lower annular rim of the upper closure cap, the sealing ring increasing in thickness downwardly from the shear zone and as it increases in thickness being devoid of abrupt changes in the contour of its walls such as would preclude axial removal of the cap and sealing ring from a non-expanding mold surrounding the sealing ring during formation in a molding process. The method comprises injecting a molten plastic into a mold shaped to form the plastic cap unit and including fixed and movable sections forming molding surfaces, disengaging the mold from the outer surface of the upper closure cap by axial movement of the related mold section relative to the remaining sections of the mold, disengaging subsequently the mold from the inner surfaces of the upper closure cap and the lower sealing ring by axial movement of the related mold section relative to the remaining fixed section of the mold still surrounding the outer wall of the sealing ring up to the lower rim of the upper closure cap, and disengaging subsequently the mold from the cap unit by axial movement of the cap unit relative to the fixed section of the mold.
It will be understood that the invention thus allows the ejection of the closure device from the mold or tool without radial opening of the mold, and in a very simple manner. In the course of the method or process as described, first an external mold part, which is a first female section, is removed from the closure cap. The closure cap thereby has enough elasticity over its total length to allow release and removal in the next step of the internal mold section, which is the male section. This is achieved by having the closure cap axially completely released over its entire periphery, because the internal thread in the closure cap makes an elastic stretching or yielding indispensable for axially removing the male section without rotation or unscrewing. This again is only possible because the closure device during this step is still held fast by the second external part, which is the second female section, in the region of the sealing ring. Since the closure cap is, of course, released completely at the outside, but is applied with its lower edge or rim on the second female mold section, the closure cap will bear firmly on the said lower edge or rim while the internal male section is withdrawn from the closure cap unit. After this step, the closure cap unit will still be held in the zone of the sealing ring by the second female mold section, but it can now readily be ejected from the mold because the internal male mold section has already released the sealing ring at the inside, and thus an inward elastic yielding of the guard ring is allowed, whereby destruction in ejection is avoided.
The apparatus of the invention is especially advantageous for production of the described closure cap in accordance with the method of the invention. For this purpose, the apparatus comprises a first female mold section having a cavity and being constructed to form the outer surface of the upper closure cap, a second female mold section having a cavity and being constructed to form the outer surface of the sealing ring and shear zone, the second female mold section being engageable with the first female mold section so as to form a combined female mold section for integrally molding the outer surfaces of the upper closure cap and the sealing ring, the second female mold section being at least partially reduced in diameter in the area engageable with the first female mold section so as to form at least the outer part of the lower annular rim of the upper closure cap, a male mold section cooperating with the first and second female mold sections and being constructed to form the inner surface of the closure cap unit, and mold operating means drivingly connected to the mold sections so as to effect, after the molding process, disengagement of the first female mold section from the closure cap by axial movement relative to the second female mold section and relative to the male mold section, disengagement of the male section from the cap unit by axial movements relative to the second female mold section, and disengagement of the second female mold section from the sealing ring by axial movement of the cap relative to the second female mold section. Preferably the male mold section includes at least one inner part or member which is axially movable against the upper inner surface of the closure cap after disengagement of the male mold section from the cap unit so as to effect disengagement of the sealing ring from the second female mold section.
The invention affords, in an optimally simple way, a new method and new apparatus for economical and rapid manufacture of plastic closure caps. The technological advance and the inventive content of the subject matter are effected not only by the novel individual features, but also by the combinations of features.
Preferred embodiments of the invention are described in detail in the ensuing description, taken with reference to the accompanying drawings.